Coupling medium for probe of ultrasonograph

ABSTRACT

PCT No. PCT/JP93/01759 Sec. 371 Date Aug. 2, 1994 Sec. 102(e) Date Aug. 2, 1994 PCT Filed Dec. 2, 1993 PCT Pub. No. WO94/12105 PCT Pub. Date Jun. 9, 1994A coupling medium for a probe of an ultrasonograph comprising a gel composed of  beta -1,3 glucan as the main component, or a gel obtained by high pressure treatment or chemical cross-linking of the same, or a gel containing  beta -1,3 glucan and a complex forming compound capable of forming a complex with  beta -1,3 glucan.

The present invention relates to coupling medium for a probe of anultrasonograph.

BACKGROUND ART

In recent years, various methods have been tried to treat diseases ofthe internal organs, without applying major surgery, so as to lightenthe physiological load on the patient and improve the progress inrecuperation. Also, even if an abdominal operation is to be performed,the detailed determination of the state of diseased areas before surgeryand determination of the internal state without having to cut open theorgan surface during surgery would give very meaningful information atthe time of actual surgery. To reply to these needs, in recent years,ultrasonography has developed and remarkably spread. The accuracy of thediagnosis using the ultrasonography before surgery has been extremelyhelpful in improving results of surgery in recent years. In particular,remarkable improvements have been made in the ability to diagnosediseases of the thyroid glands by the combination of the ultrasonographymethod and diagnosis of cells obtained by centesis and suction.

When trying to observe the internal state by placing the probe of theultrasonograph directly on the body surface or organ surface, however,it is difficult to obtain a clear image in the region within severalcentimeters from the surface due to the nature of the ultrasonograph.Further, the actual body and organ surfaces are not flat, but havecharacteristic curves and unevenness, so it is impossible to bring aninflexible probe which maintains a certain shape into close contact withthe desired location. That is, when air is present between the body andprobe, the rate of propagation of the ultrasonic waves remarkablydecreases, and an accurate image cannot be formed on the screen of thediagnostic apparatus.

To solve the above-mentioned problems, it is effective to interpose asuitable spacer (i.e., coupling medium) between the probe and body. Thecoupling medium is preferably made is the form of a sheet-like shape andis sandwiched between the probe and, for example, the body surface atthe time of diagnosis or is formed into a suitable shape capable ofbeing used by attaching to the probe directly or with a fitting. Such acoupling medium is required to have a suitable flexibility andmechanical strength and improved acoustic property (i.e., a low rate ofattenuation etc.). For example, Japanese Unexamined Patent Publication(Kokai) No. 55-63636 discloses a specific water-containing polymer gel.The gel disclosed therein, however, has problems such as an insufficientmechanical strength or a large attenuation of sound waves. Variousefforts have been made to deal with this problem. For example, there areknown a polyvinyl alcohol based polymer gel (Japanese Unexamined PatentPublication (Kokai) No. 62-298342 and Japanese Examined PatentPublication (Kokoku) No. 2-46211), a highly water absorbing resin(Japanese Unexamined Patent Publication (Kokai) No. 4-53544), andvarious organic and inorganic polymers (Japanese Examined PatentPublication (Kokoku) No. 2-21252).

These various proposed polymer gels, however, also suffer from variousproblems. Namely, media using synthetic polymers suffer from the dangerof all or part of the gel entering and remaining in the living body atthe time of centesis or surgery. Thus, there are apprehensions over thetoxicity of the gel itself or the residual monomers and therefore, thereare problems in safety. Further, natural polymers and polyvinyl alcoholgels, which are considered highly safe, are not necessarily satisfactoryin terms of their acoustic property (for example, the attenuation rateis high). To improve the acoustic property, it is necessary to increasethe water content. However, when the water content is increased, thereis the problem that the mechanical strength is decreased. Further, apolyvinyl alcohol gel tends to bleed water when pressure is applied andtherefore is not suited as a gel for a probe used pressed against thehuman body or organ surface. Further, it is poor in sterilizability(that is, it completely melts and loses its original shape under heatingat 121° C. by an autoclave, which is one of the most common method forsterilization). As a result, it is not yet commercialized. In view ofthis situation, development of a coupling medium for a probe which issafe and can be used even during centesis and surgery has been desired.

DISCLOSURE OF THE INVENTION

Accordingly, the object of the present invention is to resolve theabove-mentioned problems in the prior art and to provide a couplingmedium for a probe of a ultrasonograph which is free from problems insafety even if entering into the living body and is superior in acousticproperty, mechanical strength, and sterilizabiity.

Other objects and advantages of the present invention will be clear fromthe following description.

In accordance with the present invention, there is provided a couplingmedium for a probe of an ultrasonograph comprising a gel composed ofβ-1,3 glucan as a main component.

In accordance with there is also provided a coupling medium for a probeof an ultrasonograph obtained by subjecting a gel comprising β-1,3glucan as a main component to a high pressure treatment.

In accordance with there is further provided a coupling medium for aprobe of an ultrasonograph comprising a gel composed of β-1,3 glucan asa main component and having at least a portion of the gel chemicallycross-linked.

In accordance with the present invention, there is further provided acoupling medium for a probe of an ultrasonograph comprising a gelcomposed of β-1,3 glucan as a main component and containing a complexforming compound which can form a complex with β-1,3 glucan.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of an ultrasonographic image, in which the leftside is the image of a human neck in the case of use of the probecoupling medium prepared in Example 1--1 and the right side is the imagein the case of no use of the same.

FIG. 2 is a photograph of an ultrasonographic image, in which the rightside is the image of a human neck in the case of use of the probecoupling medium prepared in Example 1--1 and the left side is the imagein the case of use of the probe coupling medium prepared in ComparativeExample 1--1.

FIG. 3 is a graph showing the change in the breaking intensity of thegel caused by the addition of boric acid in Examples 4-1--1 and 4-1-2,obtained by dicing the curdlan gel prepared in accordance with Example4-1--1 (gel was prepared by heating at 80° C. and 121° C. forsterilization) into 20 ×20 ×10 mm pieces and using a rheometer tomeasure the breaking intensity (the points shown are the average valuesfor three measurements of the same samples).

FIG. 4 is a graph showing the change in the Young's modulus of the gelcaused by the addition of boric acid in Examples 4-1--1 and 4-1-2,obtained by dicing the curdlan gel prepared in accordance with Example4-1--1 (gel was prepared by heating at 80° C. and 121° C. forsterilization) into 20 ×20 ×10 mm pieces and using a rheometer tomeasure the Young's modulus (the points shown are the average values forthree measurements of the same samples).

FIG. 5 is a graph showing the relationship between the curdlanconcentration and the breaking intensity of the gel caused in Example4-2, obtained by dicing the curdlan gel prepared in accordance withExample 4-2 (gel was prepared by heating at 80° C. and 121° C. forsterilization) into 20 ×20 ×10 mm pieces and using a rheometer tomeasure the breaking intensity (the points shown are the average valuesfor three measurements of the same samples).

FIG. 6 is a graph showing the relationship between the curdlanconcentration and the Young's modulus of the gel caused in Example 4-2,obtained by dicing the curdlan gel prepared in accordance with Example4-2 (gel was prepared by heating at 80° C. and 121° C. forsterilization) into 20 ×20 ×10 mm pieces and using a rheometer tomeasure the Young's modulus (the points shown are the average values forthree measurements of the same samples).

FIG. 7 is a graph showing the effects of the pH on the physicalproperties (breaking intensity, Young's modulus) of the curdlan gel inExample 4-3, obtained by dicing the curdlan gel prepared in accordancewith Example 4-3 (gel was prepared by heating at 121° C. forsterilization) into 20 ×20 ×10 mm pieces and using a rheometer tomeasure the breaking intensity and the Young's modulus (the points shownare the average values for three measurements of the same samples).

Therefore, the present inventors engaged in intensive studies to solvethe above problems and, as a result, found that by using, as a probecoupling medium, a gel composed of the natural polysaccharide curdlan orother β-1,3 glucan as a main component, or a gel comprising this gelsubjected to high pressure treatment or at least partially cross-linked,or a gel containing β-1,3 glucan and a compound capable of forming acomplex with β-1,3 glucan, all of the above-mentioned problems can besolved, whereby the present invention has been completed.

That is, the β-1,3 glucan used as a starting material in the presentinvention is extremely high in safety and has the property of graduallybreaking down in the living body even if accidently remaining therein(see Yakugaku Zasshi, 110, (10) 869-875, 1990). Further, a gel preparedby adding a complex forming compound to the β-1,3 glucan can besterilized by the most common sterilization apparatuses (autoclaves) orγ-ray irradiation and therefore is extremely superior as a couplingmedium of a probe of an ultrasonograph, in particular, a probe couplingmedium used during centesis and surgery.

The constitution of the present invention will be described in detailbelow.

The concentration of the β-1,3 glucan constituting the probe couplingmedium according to the present invention is preferably 1 to 10% byweight, more preferably 2 to 5% by weight.

The probe coupling medium according to the present invention is across-linked high water content gel composed of β-1,3 glucan as a maincomponent. The β-1,3 glucan is the generic name for polysaccharideshaving glucose as structural units and β-1,3 bonded main chains. Up tothe present time, curdlan, scleroglucan, sclerotan, schizophyllan,lentinan, paramiron, calose, laminalan, and many others are known. Amongthese, curdlan is supplied to the market stably and at a relatively lowprice and is considered most suited as a material for a probe couplingmedium.

Curdlan is described in the Nihon Shokuhin Kogyo Gakkaishi, Vol. 38, No.8, 736-742 (1991) etc. and is one kind type of polysaccharides producedby microorganisms (Alcaligenes faecalis var. myxogenes or many strainsof Agrobacterium and Rizobium) and only has D-glucose as a constituentsaccharide. 99% or more of the glucoside bonds are β-1,3 bonds. Curdlanis insoluble in water, but dissolves in aqueous alkaline solutions ofsodium hydroxide etc. A curdlan dispersion may be obtained as ahomogeneous dispersion by adding water to a curdlan powder andvigorously agitating this by a high speed homogenizer or cutter mixeretc. or adding curdlan to warm water of about 55° C., while agitatingmanually or by a propeller type agitator etc., then cooling.

This aqueous dispersion forms a gel upon heating. The gel obtained bythe heating may be classified into two main types depending on thetreatment temperature. That is, there are a heat-irreversible gelobtained by heating at least at 80° C. and a heat reversible gelobtained by heating at about 60° C. and then cooling. These arerespectively called a high set gel and low set gel.

It is also possible to prepare the gel without heating by dissolving thecurdlan in an aqueous alkaline solution, allowing this to stand, andneutralizing by carbon dioxgen gas etc. or using a dialysis membrane toremove the sodium hydroxide. Further, it is possible to form a gel byadding, to the aqueous alkaline solution, calcium, magnesium ions, andother cations to form a cross-linked structure by the freed hydroxylgroups and cations.

β-1,3 glucans other than curdlan may also be made to form a gel inaccordance with the above-mentioned method.

The method of manufacture of a probe coupling medium according to thepresent invention may be any method so long as a gel is obtained whichis composed of curdlan or another β-1,3 glucan as a main component, hasa water content of at least 80% by weight, and does not contain airbubbles. The method of manufacture is not particularly limited.

For example, describing two or three methods of preparation takingcurdlan as an example, first the above-mentioned aqueous dispersion ofcurdlan is prepared.

The concentration of the curdlan is 1 to 10% by weight, preferably 2 to5% by weight. Even if less than 1% by weight, a gel can be prepared, butthe strength of the prepared gel is remarkably low. The gel breaks evenwith application of a slight force, making handling inconvenient.Therefore, substantially it is preferable to prepare it with aconcentration of at least 2% by weight. In the same way, a gel can beprepared even with a concentration of more than 10% by weight, but theviscosity at the time of dispersion of the curdlan becomes extremelyhigh and the subsequent deaeration procedure becomes difficult. Further,the modulus of the gel prepared becomes too high, the ability of closecontact with the human body surface is impaired, and thus the gelbecomes unsuitable for ultrasonography. For actual diagnosis, a gelprepared with a concentration of not more than 5% by weight is suitable.

The prepared dispersion is sufficiently deaerated under a vacuum andpoured gently on to a flat plate or a shaping mold. This is heated at atemperature of at least 60° C., preferably at least 80° C., in a heatsterilization apparatus or hot water bath preferably for at least 10minutes to cause the gelation. After cooling, a sterilization procedureis followed involving reheating or irradiation to obtain a stronger gel.The longer heating time and the higher heating temperature is, thestronger the gel become.

As the method for preparing the neutralized gel, curdlan powder isdissolved in an aqueous alkaline solution, for example, 1-10% by weightof the curdlan powder in a 5 mM or more, preferably 10-500 mM, aqueoussolution of sodium hydroxide. The resultant solution is deaerated undera vacuum, then an equimolar aqueous solution of hydrochloric acid isgently poured in. The resultant solution is allowed to stand forneutralization. At this time, it is possible to easily judge from theouter appearance if the inside has been neutralized by the state ofgelation and turbidity accompanying the neutralization. The neutralizedcurdlan gel thus obtained may be heated at a temperature of at least 60°C., preferably at least 80° C., so as to make the gel stronger.

The above-mentioned methods of preparing a gel may be performed alone orin any combination thereof.

The probe coupling medium of the present invention may contain therein,in addition to the β-1,3 glucans such as curdlan, which are the maincomponent of the gel, one or more substances from among other polymersubstances (for example, alginic acid, carrageenan, agar--agar,glucomannan, starch, hyaluronic acid, cellulose, methylcellulose,ethylcellulose, nitrocellulose, and polyvinyl alcohols), various typesof salts (for example, sodium salts or potassium salts of phosphoricacid, acetic acid, lactic acid, citric acid, and boric acid and sodiumchloride), various types of saccharides (for example, glucose, sucrose,maltose, galactose, mannose, lactose, etc.), urea, glycerin, andsilicone, so as to obtain a gel exhibiting more superiorcharacteristics.

The gel thus prepared has a suitable flexibility and is extremely easyto shape and thus is extremely advantageous when thinking of theconnection between a probe having a certain shape and a coupling medium.The gel thus prepared displays all excellent acoustic property. That is,the sound velocity is 1497 to 1504 m/s, close to the case of water, andthe attenuation rate is 0.06 to 0.16 dB/MHz•cm, the lowest attenuationrate in gels for coupler known today. Further, when the mechanicalstrength of the gel was measured, it was found that the breakingintensity was 5.37×10² to 4.22×10³ g/cm² and the Young's modulus was1.96×10⁶ to 6.71×10⁶ dyn/cm². This shows that the gel has sufficientstrength for use as a probe coupling medium.

The probe coupling medium according to the second aspect of the presentinvention is a gel comprising curdlan or another β-1,3 glucan as themain component and having a water content of at least 80% by weight andis obtained by performing high pressure treatment after gelation byheat. Sometimes, the gel may be reheated for sterilization andimprovement of the gel strength.

Next, an example of the manufacturing process will be explained. First,the above-mentioned curdlan-water dispersion is prepared. Theconcentration of the curdlan is from 1 to 10% by weight, preferably 2 to5% by weight. The dispersion is deaerated under a vacuum, then gentlypoured on a plate or in a shaping mold and once again fully deaeratedunder a vacuum. The result is heated by a heat sterilization apparatusor in a hot water bath to a temperature of at least 60° C., preferablyat least 80° C., preferably for at least 10 minutes. After cooling, theresultant gel is subjected to a high pressure treatment of at least 100kg/cm², preferably at least 1000 kg/cm², then is heated at a temperatureof at least 60° C., preferably at least 80° C., for preferably at least10 minutes or is irradiated with radiation for sterilization, wherebythe stronger gel is obtained. The longer heating time and the higherheating temperature is, the stronger the gel become.

Recently, a method has been disclosed of increasing the gel strength bysubjecting an aqueous dispersion of curdlan to a high pressuretreatment, followed by heat treating (see Japanese Unexamined PatentPublication (Kokai) No. 4-158752), but the mechanism thereof is stillnot clear.

The coupling medium used during centesis and surgery must be sterile instate at the time of use. Toward this end, for the sterilization of thecoupling medium, it is desirable to perform the sterilization operationsimply in hospitals and to use the most popular heat sterilizationapparatus (autoclave).

The powder of the curdlan (for example, curdlan made by Takeda ChemicalIndustries, Ltd.) being used at the food level contains several kinds ofimpurities derived from the medium and microorganisms. Also, the powderis slightly brownish. As the starting material for a coupling mediumused for centesis or surgery, it is only naturally desirable to use ahighly refined starting material which does not include such impurities.However, if such a refined curdlan powder (for example, Curdlan SDS madeby Takeda Chemical Industries, Ltd.) is used to prepare a gel byheating, there might be happened cracking and fracturing in the gelalong with the increase in temperature (mostly over 100° C.). Note thatCurdlan SDS consists of curdlan which has been refined to removeimpurities.

The cause for the cracking and fracturing is thought to be thecrystallization of curdlan molecules along with heating. To suppressthis crystallization, the general practice has been to add othersubstances. In the case of curdlan, it is difficult to prepare a mixturecompletely homogeneous on the molecular level since that substance isinsoluble in water. Therefore, it has been extremely difficult to avoidcracks and fractures in the refined curdlan gel up to now.

By performing the above-mentioned pressure treatment (100 kg/cm² ormore, preferably 1000 to 10,000 kg/cm²), however, it has become possibleto resolve the problem of cracking and fracturing accompanying heating.The method of the pressure treatment may be any one which gives a highpressure of at least 100 kg/cm². In recent years, Mitsubishi HeavyIndustries, Ltd., has marketed an apparatus which can perform highpressure treatment at any temperature. As the procedure for the pressuretreatment, rather than the heating and gelation after the pressuretreatment of the curdlan dispersion as in Japanese Unexamined PatentPublication (Kokai) No. 4-158752, the method of pressure treatment afterheating and gelation at a temperature at which cracking and fracturingdo not occur, preferably 60° to 100° C., is preferable and a highresistance to fracturing along with heating can be obtained. Thetemperature at the time of the pressure treatment does not have to beless than the gelation temperature, since gelation has already occurred,and can be set to any temperature.

The concentration of the curdlan may be any concentration giving ahomogeneous dispersion, but 1 to 10% by weight, preferably 2 to 5% byweight, is desirable. When the concentration is less than 1% by weight,the strength of the prepared gel is insufficient, while when more than10% by weight, the viscosity of the dispersion becomes extremely highand it becomes difficult to obtain a homogeneous gel not including airbubbles. Further, when the gel is used as a coupling medium, a highwater content is required to give superior acoustic property and thecurdlan concentration is desirably no more than 5% by weight. Even witha concentration of 2 to 5% by weight, the strength of the gel issufficient and the gel will not break even in procedures pressing itagainst the body surface and deforming it.

The probe coupling medium of the present invention may contain therein,in addition to β-1,3 glucans such as curdlan, i.e., the main componentof the gel, one or more substances from among other polymer substances(for example, alginic acid, carrageenan, agar--agar, glucomannan,starch, hyaronic acid, cellulose, methylcellulose, ethylcellulose,nitrocellulose, and polyvinyl alcohols), various types of salts (forexample, sodium salts or potassium salts of phosphoric acid, aceticacid, lactic acid, citric acid, and boric acid and sodium chloride),various types of saccharides (for example, glucose, sucrose, maltose,galactose, mannose, lactose, etc.), urea, glycerin, and silicone, so asto obtain a gel exhibiting more superior characteristics.

The gel thus prepared has a suitable flexibility and is extremely easyto shape and thus is extremely advantageous when thinking of connectionbetween a probe having a certain shape and a coupling medium. The gelthus prepared displays all excellent acoustic property. That is, thesound velocity is 1490 to 1543 m/s, close to the case of water, and theattenuation rate is 0.05 to 0.23 dB/MHz•cm, the lowest attenuation ratein gels for coupler known today. Further, when the mechanical strengthof the gel was measured, it was found that the breaking intensity was5.91×10² to 4.64×10³ g/cm² and the Young's modulus was 2.16×10⁶ to7.38×10⁶ dyn/cm². This shows that the gel has sufficient strength foruse as a probe intensity medium.

The probe intensity medium according to the third aspect of the presentinvention is obtained by adding a suitable cross-linking agent to theaqueous alkaline solution of β-1,3 glucan such as curdlan when gelatingthe curdlan so as to cause cross-linking. For example, 1 to 10% byweight of curdlan powder is added to a 5 mM or more, preferably 25 to100 mM, aqueous solution of sodium hydroxide, after 0.001 to 2% byweight of a cross-linking agent is added, the resultant solution issufficiently agitated, and then this is poured into a mold anddeaerated. This is allowed to stand at room temperature or is heated atleast at 50° C. to cause the cross-linking reaction. After the gelation,the gel is taken out from the mold and neutralized in an equimolaraqueous solution of hydrochloric acid, then is fully washed with water.The heating and washing enable the complete removal of the unreactedcross-linking agent. Further, by heat treatment at least at 60° C.,preferably 100 to 121° C., a stronger gelation is possible. Thecross-linking agent used here may by any which has at least twofunctional groups capable of reacting with hydroxyl groups or carboxylgroups per molecule. For example, one or more of a polyhydricglycidylether compound, a polyhydric aziridine compound, a polyhydricamine compound, a polyhydric isocyanate compound, a halomethyl oxiranecompound and aldehydes, and divinyl sulfone may be used.

As the polyhydric glycidyl ether compound, there are(poly)ethyleneglycol glycidyl ethers, glycerol polyglycidyl ethers, etc.As the polyhydric aziridine compound, there are2,2-bishydroxymethylbutanol-tris[3(1-aziridinyl)propionate],1,6-hexamethylenediethyleneurea,diphenylmethane-bis-4,4'-N,N'-diethyleneurea, etc. As the polyhydricamine compound, there are ethylene diamine, diethylene triamine,triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine,polyethylene imine, etc. As the polyhydric isocyanate compound, thereare 2,4-tolylene diisocyanate, hexamethylene diisocyanate, etc. As thehalomethyl oxirane compound, there are epichlorohydrin, epibromohydrin,β-methylepichlorohydrin, β-methylepibromohydrin, etc.

The probe coupling medium of the present invention may contains therein,in addition to the β-1,3 glucan such as curdlan as the main component ofthe gel, one or more substances from among other polymer substances (forexample, alginic acid, carrageenan, agar--agar, glucomannan, starch,hyaluronic acid, cellulose, methylcellulose, ethylcellulose,nitrocellulose, and polyvinyl alcohols), various types of salts (forexample, sodium salts or potassium salts of phosphoric acid, aceticacid, lactic acid, citric acid, and boric acid and sodium chloride),various types of saccharides (for example, glucose, sucrose, maltose,galactose, mannose, lactose, etc.), urea, glycerin, and silicone, so asto obtain a gel exhibiting more superior characteristics.

The gel thus prepared has a suitable flexibility and is extremely easyto shape and thus is extremely advantageous when thinking of connectionbetween a probe having a certain shape and a coupling medium. The gelthus prepared displays all excellent acoustic property. That is, thesound velocity is 1499 to 1510 m/s, close to the case of water, and theattenuation rate is 0.07 to 0.20 dB/MHz•cm, the lowest attenuation ratein gels for coupler known today. Further, when the mechanical strengthof the gel was measured, it was found that the breaking strength was1.281×10³ to 7.601×10³ g/cm² and the Young's modulus was 2.671×10⁶ to9.318×10⁶ dyn/cm². This shows that the gel has sufficient strength foruse as a probe coupling medium.

According to the fourth aspect of the present invention, there isprovided a coupling medium for a probe of an ultrasonograph comprising agel composed of β-1,3 glucan and a complex forming compound.

The concentration of the complex forming compound is preferably 5 to 900mM. As specific examples of the complex forming compound making up partof the probe coupling medium according to the present invention, mentionmay be made of boric acid, borax, phenylboric acid, sulfonatedphenylboric acid, germanic acid, molybdic acid, etc. These may be usedalone or any as mixtures of two or more types.

The coupling medium used during centesis and surgery must be sterile instate at the time of use. Toward this end, for the sterilization of thecoupling medium, it is desirable to perform the sterilization operationsimply in the hospital and to use the most popular type of heatsterilization apparatus (autoclave). However, when a gel of curdlan isheat sterilized, the gel becomes turbid along with the increase intemperature (in most cases over 100° C.). When this is used as thecoupling medium for a probe for an ultrasonograph, the resultantultrasonographic image was hazy and unclear in state.

The above turbidity is considered to be caused by the crystallization ofcurdlan molecules along with heating. To suppress this crystallization,the general practice has been to add other substances. In the case ofcurdlan, it is difficult to prepare a mixture completely homogeneous onthe molecular level since that substance is insoluble in water.Therefore, it has been extremely difficult to avoid turbidity of thecurdlan gel by general additives up to now. However, it became possiblein accordance with the present invention to solve the problem of theturbidity of the gel along with heating by adding the above-mentionedcomplex forming compound.

The concentration of the β-1,3 glucan such as curdlan in accordance withthe present invention is not particularly limited so long as it is aconcentration by which a homogeneous dispersion may be obtained, but ispreferably 1 to 10% by weight, more preferably 2 to 5% by weight. With aconcentration of curdlan less than 1% by weight, the strength of theprepared gel sometimes becomes insufficient, while when over 10% byweight, the viscosity of the dispersion becomes high and it becomesdifficult to obtain a homogeneous gel not containing air bubbles.Further, when the gel composed of β-1,3 glucan as a main componentaccording to the present invention is used as a coupling medium, a highwater content is required to give superior acoustic property and theβ-1,3 glucan concentration is desirably not more than 5% by weight. Notethat even with a concentration of β-1,3 glucan of 2 to 5% by weight, thestrength of the gel is sufficient and the gel will not break even inprocedures pressing it against the human body surface and deforming it.

The complex forming compound used in the present invention, asrepresented by boric acid or boric acid salts, is known to react easilyand quickly with saccharides and polyoxy compounds related to the sameand to form complex compounds having negative charges (Nature, 161, 96,1948). As other complex forming compounds, there are known phenylboricacid, sulfonated phenylboric acid, germanic acid, and molybdic acid. Theamount of these added is for example preferably 5 to 900 mM (number ofmillimoles of complex forming compound in one liter of gel), morepreferably 30 to 400 mM in range. When the amount added is less than 5mM, there is a tendency for a lesser effect of improvement of thephysical properties and transparency, while conversely when the amountis over 400 mM, not that much greater an effect of improvement can beexpected. When the amount is over 900 mM, dissolution becomes difficult.Further, if considering the use of the gel in centesis and surgery, theamount of the complex forming compound added is preferably approximatelythe isotonic concentration. The transparency of the gel which isprepared depends on the pH of the added boric acid solution. Under weakalkaline conditions, the reaction proceeds, the rate of production ofthe complex compound becomes higher, and the transparency of the gel isimproved as well. However, when considering the use of the couplingmedium of the present invention in centesis and surgery, the pH ispreferably around 7.4, close to that of blood.

The probe coupling medium of the present invention may contain therein,in addition to the β-1,3 glucan, i.e., the main component, other polymersubstances (for example, alginic acid, carrageenan, agar--agar,glucomannan, starch, hyaluronic acid, cellulose, methylcellulose,ethylcellulose, nitrocellulose, and polyvinyl alcohols), various typesof salts (for example, sodium salts or potassium salts of phosphoricacid, acetic acid, lactic acid, and citric acid and sodium chloride),various types of saccharides (for example, glucose, sucrose, maltose,galactose, mannose, lactose, etc.), urea, glycerin, and silicone inaccordance with need either alone or as mixtures of two or more so as toobtain a gel exhibiting more superior characteristics.

The gel thus prepared has a suitable flexibility and is extremely easyto shape and thus is extremely advantageous when thinking of connectionbetween a probe having a certain shape and a coupling medium. The gelthus prepared displays all excellent acoustic property. That is, thesound velocity is 1499 to 1540 m/s, close to the case of water, and theattenuation rate is 0.06 to 0.20 dB/MHz•cm. Further, when the mechanicalstrength of the gel was measured, it was found that the breakingintensity was 5.43×10² to 1.32×10⁴ g/cm² and the Young's modulus was1.49×10⁶ to 1.57×10⁷ dyn/cm². This shows that the gel has sufficientstrength for use as a probe coupling medium.

EXAMPLES

The present invention will now be explained in further detail by, but isby no means limited to, the following Examples.

Example 1--1

Ninety-seven parts by weight of water were added to 3 parts by weight ofcurdlan powder (Takeda Chemical Industries, Ltd.) and the mixture wasagitated for 10 minutes by a high speed homogenizer (made by NipponSeiki Co, Ltd., Power Homogenizer, PM-1). The above aqueous curdlandispersion was sufficiently deaerated under a vacuum, then was pouredinto a mold and heated at 100° C. for 10 minutes for gelation. This wascooled and taken out from the mold, then was heated at 121° C. for 20minutes in a heat sterilizer (made by Tomy Seiko; autoclave, SS-245).This operation enabled complete gelation and sterilizationsimultaneously. The obtained probe coupling medium was 100 mm in length,50 mm in width, and 15 mm in thickness.

The probe coupling medium thus prepared was measured for its acousticproperty, as a result of which values of a sound velocity of 1499 m/sand an attenuation of 0.12 dB/MHz•cm were obtained. Further, a rheometer(made by Fudo Kogyo Co.; NRM-2010J-CW) was used to measure the physicalproperties, whereupon a breaking intensity of 1.80×10³ g/cm² and Young'smodulus of 3.84×10⁶ dyn/cm² were displayed. Next, the above-mentionedcoupling medium was placed between the probe of an ultrasonograph (madeby Aloka Co.; SSD-2000) and the skin for image diagnosis, whereupon aclearer sharper image (FIG. 1) was obtained compared with the case of nocoupling medium interposed.

Comparative Example 1--1 (See Description of Japanese Examined PatentPublication (Kokoku) No. 62-298342)

A 10% aqueous solution of polyvinyl alcohol with an average degree ofpolymerization of 1000 and degree of saponification of 87% poured into aflat plate of a thickness of 15 mm and then was frozen at-30° C.,followed by thawing. This freezing and thawing operation was repeated 8times to obtain a gel with a water content of 90%. The gel was measuredfor the sound velocity and attenuation in accordance with Example 1--1.As a result, the sound velocity was 1500 m/s, about the same as inExample 1--1, but the attenuation rate was 1.0 dB/MHz•cm, about 10 timeshigher, which is not sufficient for the probe coupling medium of anultrasonograph. An ultrasonographic image obtained using this couplingmedium is shown in FIG. 2.

Comparative Example 1-2 (See Japanese Examined Patent Publication(Kokoku) No. 1-288243)

A 3% aqueous solution of polyvinyl alcohol having an average degree ofpolymerization of 1500 and a degree of sapurification of 95% was heatedat 80° C. to dissolve, placed in a vacuum heating and agitationapparatus for deaeration, allowed to cool to 50° C., cooled to-30° C. tofreeze it, then was warmed to room temperature to thaw it. This freezingand thawing operation was repeated 9 times to obtain a gel with a watercontent of 97%. When the gel was heated and sterilized at 121° C. for 20minutes in the same way as in Example 1--1, it melted and could notmaintain its original shape. As opposed to this, the curdlan gel shownin Example 1--1 showed no deformation due to heating at 121° C. for 20minutes and showed no change in acoustic property either.

Comparative Example 1-3 (See Japanese Examined Patent Publication(Kokoku) No. 2-21252)

One thousand milliliters of an aqueous solution containing 150 g ofacrylamide monomer and 8 g of N,N-methylene bisacrylamide was prepared.To this solution were added 100 ml of a 5% aqueous solution ofdimethylaminopropionitrile and 100 ml of 1% potassium persulfate. Thesewere mixed well while taking care not to cause entrainment of airbubbles, then the result was immediately poured into a container of alength of 10 cm, a width of 15 cm, and a depth of 10 cm and caused toreact at 40° C. for 10 hours. The gel prepared in this manner containedresidual amounts of unreacted acrylamide monomer, whose toxicity is amatter of concern when using the gel for ultrasonography.

Comparative Example 1-4 (See Japanese Unexamined Patent Publication(Kokai) No. 55-63636)

To 100 parts by weight of ordinary temperature water was added 8 partsby weight of a hydrophilic polyurethane having an 80/20 ratio ofcopolymerization of ethylene oxide and propylene oxide and a 2/4 ratioof --OH of the copolymer and --NCO of the tolylene diisocyanate, whichwas quickly homogeneously dispersed. The result was immediately pouredinto a polypropylene container and allowed to stand in that state for 30minutes to obtain a polyurethane type water containing gel. The gelprepared in the above way contained a residual amount of unreactedethylene oxide. Ethylene oxide used for gas sterilization as well has inrecent years been considered a matter of concern due to the toxicitycaused by residual presence. The gel prepared in the above mannertherefore has been considered unsuitable as a coupling medium for aprobe of an ultrasonograph.

Example 1-2

Probe contact media were prepared by using isotonic aqueous solutions ofsodium chloride instead of the water in the above Example and further byadjusting the curdlan concentration from 2 to 5%. By adding salt in thisway, it became possible to prevent deterioration of the gel duringstorage compared with the case of water. Further, no reduction wasobserved at all in the acoustic property due to the addition of the salt(Table 1--1). Clear ultrasonographic images were obtained by the use ofthe above probe coupling media.

                  TABLE 1-1                                                       ______________________________________                                        Effects of Salt on Acoustic Property of                                       Curdlan Gel                                                                            Curdlan      Sound    Attenuation                                    Prepared concentration                                                                              velocity rate                                           solution (wt %)       (m/s)    (dB/MHz · cm)                         ______________________________________                                        Water    2            1497     0.06                                                    3            1499     0.12                                                    4            1501     0.14                                                    5            1504     0.16                                           Physiological                                                                          2            1508     0.07                                           saline   3            1512     0.08                                           solution 4            1513     0.13                                                    5            1519     0.16                                           ______________________________________                                    

Example 1-3

Ninety-seven parts by weight of water were added to 2.7 parts by weightof curdlan and 0.3 part by weight of alginic acid and the mixture wasagitated at 13,000 rpm for 5 minutes by a high speed homogenizer. Themixture was sufficiently deaerated under a vacuum, then was poured intoa mold and heated at 100° C. for 10 minutes for gelation. The gel wascooled and taken out from the mold, then was immersed in a 10% calciumchloride solution for gelation of the alginic acid. After 24 hours, thegel was taken out, washed with water, then heated at 121° C. for 20minutes in a heat sterilizer to perform complete gelation andsterilization simultaneously. The probe coupling medium thus preparedwas used for ultrasonography, whereupon a clearer sharper image wasobtained compared with the case of no coupling medium used.

Example 1-4

Three parts by weight of the additives shown in the following table wereadded to 7 parts by weight amounts of curdlan, then 90 parts by weightof water were added and the results were agitated at 10,000 rpm for 10minutes in a high speed homogenizer. The results were deaerated under avacuum, then poured gently on a flat plate and heated at 100° C. for 10minutes for gelation. The results of observation of the thus preparedgels and the results of the diagnosis of the ultrasonographic images areshown in Table 1-2.

                  TABLE 1-2                                                       ______________________________________                                        Effect of Addition of Additives                                                           Result of     Ultrasonographic                                    Additive    observation   image                                               ______________________________________                                        Starch      Good          Good                                                Polyvinyl alcohol                                                                         Some stickiness on                                                                          Good                                                            surface                                                           Carrageenan Good          Good                                                Methylcellulose                                                                           Some stickiness on                                                                          Good                                                            surface                                                           Scleroglucan                                                                              Yellow, good  Good                                                ______________________________________                                    

Example 1-5

Three parts by weight of curdlan powder were dissolved in 97 parts byweight of a 150 mM sodium hydroxide solution. The resultant mixture wasdeaerated under a vacuum, then an equal amount of an aqueous solution of150 mM hydrochloric acid was gently poured in from above. The result wasallowed to stand for 48 hours for neutralization. After theneutralization, the gel was taken out and washed with physiologicalsaline solution so as to obtain the probe coupling medium. It becameclear that a clear image could be obtained by ultrasonography using thisprobe coupling medium.

Example 1-6

Ninety-four parts by weight of a physiological saline solution wereadded to 6 parts by weight of curdlan and the mixture was agitated for10 minutes by a high speed homogenizer. The resultant mixture andmixture was deaerated under a vacuum, then heated at 100° C. for 10minutes for gelation. The result was cooled and taken out from the mold,then was placed in a container filled with a physiological salinesolution and irradiated with gamma rays for sterilization. The physicalproperties of the obtained probe coupling medium were a breakingstrength of 5.23×10³ g/cm² and a Young's modulus of 7.23×10⁶ dyn/cm².The probe coupling medium was used for ultrasonography, whereupon aclearer sharper image was obtained compared with the case of no couplingmedium interposed.

Example 1-7

Ninety-seven parts by weight of urea solutions of the concentrationsshown in the following table were added to 3 parts by weight of curdlanpowder and the mixtures were agitated for 10 minutes by a high speedhomogenizer. The above aqueous curdlan dispersions were sufficientlydeaerated under a vacuum, then were poured into molds and heated at 100°C. for 10 minutes for gelation. These were cooled and taken out from themolds, then were heated at 121° C. for 20 minutes in a heat sterilizer.This operation enabled complete gelation and sterilizationsimultaneously. The breaking intensity and Young's modulus are shown inTable 1-3. The above-mentioned coupling media were placed between theprobe of an ultrasonograph and the skin for image diagnosis, whereuponclearer sharper images were obtained compared with the case of nocontact media interposed.

                  TABLE 1-3                                                       ______________________________________                                        Effect of Addition of Urea                                                    Urea                                                                          concentration                                                                             Breaking intensity                                                                         Young's modulus                                      (mM)        (×10.sup.3 g/cm.sup.2)                                                               (×10.sup.6 dyn/cm.sup.2)                       ______________________________________                                         10         1.70         4.44                                                  50         2.49         4.97                                                 100         2.98         4.20                                                 500         1.50         1.99                                                 ______________________________________                                    

Example 1-8

Ninety-six point five part by weight amounts of glucose and sucroseaqueous solutions shown in the following Table were added to 3.5 partsby weight of curdlan powder and the mixtures were agitated for 10minutes by a high speed homogenizer. The above curdlan dispersions weresufficiently deaerated under a vacuum, then were poured into molds andheated at 100° C. for 10 minutes for gelation. These were cooled andtaken out from the molds, then were heated at 121° C. for 20 minutes ina heat sterilizer. This operation enabled complete gelation andsterilization simultaneously. The breaking intensity and Young's modulusare shown in Table 1-4. The above-mentioned contact media were placedbetween the probe of an ultrasonograph and the skin for image diagnosis,whereupon clearer sharper images were obtained compared with the case ofno contact media interposed.

                  TABLE 1-4                                                       ______________________________________                                        Effect of Addition of Saccharide                                              Aqueous saccharide                                                                           Breaking                                                       solution       intensity  Young's modulus                                     (concentration; mM)                                                                          (×10.sup.3 g/cm.sup.2)                                                             (×10.sup.6 g/cm.sup.2)                        ______________________________________                                        Glucose (75)   3.41       7.10                                                Glucose (150)  3.12       6.51                                                Sucrose (75)   2.24       5.48                                                Sucrose (150)  2.68       5.52                                                ______________________________________                                    

Example 1-9

Ninety-six point five parts by weight of an 150 mM aqueous solution ofsodium lactate were added to 3.5 parts by weight of curdlan and themixture was agitated for 10 minutes by a high speed homogenizer. Theabove aqueous curdlan dispersion was sufficiently deaerated under avacuum, then was poured into a mold and heated at 100° C. for 10 minutesfor gelation. This was cooled and taken out from the mold, then washeated at 121° C. for 20 minutes in a heat sterilizer. This operationenabled complete gelation and sterilization simultaneously. The couplingmedium was placed between the probe of an ultrasonograph and the skinfor image diagnosis, whereupon a clearer sharper image was obtainedcompared with the case of no coupling medium interposed.

Example 1-10

Ten grams of scleroglucan (made by San-Ei Gen F.F.I. Inc.) weredissolved in 10 liters of 0.03M NaIO₄ and the resultant mixture wasallowed to stand at 5° C. for five days. Next, 500 ml of ethylene glycolwas added and the mixture agitated, then dialysis was performed at 5° C.for two days. Ammonia water was added to the dialyzed solution to makeit weakly alkaline, then 5 g of NaBH₄ were added and the mixture wasallowed to stand. Next, this was neutralized by 1N acetic acid, thenonce again dialyzed against flowing water at 5° C. and evaporated todryness. The powder thus prepared was digested by β-1,3 glucanase, thenthe decomposed product solution was spotted on No. 50 filter paper (madeby Toyo Roshi Kaisha, Ltd.) and developed byn-butanol/isopropanol/water=3:12:4, whereupon it became clear that theproduct was curdlan-like β-1,3 glucan with about 95% of the β-1,6 bondside chains removed.

Ninety-two parts by weight of physiological saline solution were addedto 8 parts by weight of this product and the mixture was agitated for 10minutes by a high speed homogenizer (made by Nippon Seiki Co.; PowerHomogenizer, PM-1). The mixture was sufficiently deaerated under avacuum, then was poured into a mold and heated at 80° C. for 10 minutesfor gelation. This was cooled and taken out from the mold, then washeated at 121° C. for 20 minutes in a heat sterilizer (made by TomySeiko, autoclave, SS-245), whereby complete gelation and sterilizationwere performed.

The coupling medium thus prepared was measured for its acousticproperty, as a result of which values of a sound velocity of 1510 m/sand an attenuation rate of 0.19 dB/MHz•cm were obtained. Further, arheometer (made by Fudo Kogyo Co.; NRM-2010J-CW) was used to measure thephysical properties, whereupon a breaking intensity of 4.50×10³ g/cm²and Young's modulus of 7.84×10⁶ dyn/cm² were displayed.

The obtained probe coupling medium was used for ultrasonography,whereupon a clearer sharper image was obtained compared with the case ofno coupling medium used.

Example 1-11

One gram of Schizophyllan (Gakken Seiyaku K.K.) was used and the sameprocedure followed on a scale of 1/10th that of the above Example 1-10to cut the branch side chains. Thus, it becomes clear that the productwas curdlan-like β-1,3 glucan with about 93% of the β-1,6 bond sidechains removed.

Ninety-five parts by weight of a physiological saline solution wereadded to 5 parts by weight of this product and the mixture was agitatedfor 10 minutes by a high speed homogenizer. The mixture was sufficientlydeaerated under a vacuum, then was poured into a mold and heated at 100°C. for 20 minutes for gelation. This was cooled and taken out from themold, then was heated at 121° C. for 20 minutes in a heat sterilizer,whereby complete gelation and sterilization were performed.

The coupling medium thus prepared was measured for its acousticproperty, as a result of which values of a sound velocity of 1501 m/sand an attenuation rate of 0.15 dB/MHz•cm were obtained. Further, arheometer was used to measure the physical properties, whereupon abreaking intensity of 3.20×10³ g/cm² and Young's modulus of 5.56×10⁶dyn/cm² were displayed. The probe coupling medium thus obtained was usedfor ultrasonography, whereupon a clearer sharper image was obtainedcompared with the case of no coupling medium used.

Example 2-1--1

Ninety-six point five parts by weight of water were added to 3.5 partsby weight of Curdlan SDS (made by Takeda Chemical Industries, Ltd.) andthe mixture was agitated for 10 minutes by a high speed homogenizer. Theabove aqueous curdlan dispersion was sufficiently deaerated under avacuum, then was poured into a mold and heated at 100° C. for 10 minutesfor gelation. This was cooled and taken out from the mold, then waspacked into a heat seal pack and treated at 21° C. and 3000 kg/cm² for10 minutes in a high pressure treatment apparatus. Then, this was heatedat 121° C. for 20 minutes in a heat sterilizer. This operation enabledcomplete gelation and sterilization simultaneously.

The probe coupling medium thus prepared was measured for its acousticproperty, as a result of which values of a sound velocity of 1502 m/sand an attenuation of 0.14 dB/MHz•cm were obtained. Further, a rheometer(made by Fudo Kogyo Co.; NRM-2010J-CW) was used to measure the physicalproperties, whereupon a breaking strength of 2.97×10³ g/cm² and Young'smodulus of 5.19×10⁶ dyn/cm² were displayed. Next, the above-mentionedprobe coupling medium was placed between the probe of an ultrasonographand the skin for image diagnosis, whereupon a clearer sharper image wasobtained compared with the case of no coupling medium interposed.

Example 2-1-2

Exactly the same procedure was followed as in Example 2-1--1 to obtain acurdlan gel except for the high pressure treatment. When heated at 121°C. for 20 minutes, three out of 10 samples of the gel showed cracks andfractures and therefore the heat resistance was insufficient for acoupling medium of a probe of an ultrasonograph. As opposed to this, noteven one sample out of 10 of the high pressure treated gel of Example2-1--1 showed any cracks or fractures even when repeated treated at 121°C. for 20 minutes, so the heat resistance was clearly improved.

Example 2-1-3

A 3.5% curdlan dispersion was prepared and deaerated in accordance withExample 2-1--1. The dispersion was packed into a heat seal pack andtreated at 21° C., 3000 kg/cm², and 10 minutes by a high pressuretreatment apparatus. Then, the treated dispersion was gently poured intoa mold and heated at 100° C. for 10 minutes for gelation. This wascooled, then taken out from the mold. Next, the gel was sterilized byheating at 121° C. for 20 minutes, whereupon two out of 10 samplesshowed cracks and fractures. Therefore, the heat resistance was notsufficient for a coupling medium for a probe of an ultrasonograph.

Example 2--2

Probe coupling media were prepared by using isotonic aqueous solutionsof sodium chloride instead of the water in the above example and furtherby adjusting the curdlan concentration from 2 to 5%. By adding salt inthis way, it became possible to prevent deterioration of the gel duringstorage compared with the case of water. Further, no reduction wasobserved at all in the acoustic property due to the addition of the salt(Table 2-1). Clear ultrasonographic images were obtained by the use ofthe above probe coupling mediums.

                  TABLE 2-1                                                       ______________________________________                                        Effects of Salt on Acoustic Property of                                       Curdlan Gel                                                                            Curdlan      Sound    Attenuation                                    Prepared concentration                                                                              velocity rate                                           solution (wt %)       (m/s)    (dB/MHz · cm)                         ______________________________________                                        Water    2            1495     0.07                                                    3            1498     0.09                                                    4            1508     0.13                                                    5            1507     0.16                                           Physiological                                                                          2            1510     0.08                                           saline   3            1515     0.09                                           solution 4            1519     0.14                                                    5            1522     0.17                                           ______________________________________                                    

Example 2-3

Ninety-two point seven parts by weight of water were added to 7 parts byweight of Curdlan SDS and 0.3 part by weight of alginic acid and themixture was agitated at 13,000 rpm for 5 minutes by a high speedhomogenizer. This was sufficiently deaerated under a vacuum, then waspoured into a mold and heated at 100° C. for 10 minutes for gelation.The gel was cooled and taken out from the mold, then was immersed in a10 percent calcium chloride solution for gelation of the alginic acid.After 24 hours, the gel was taken out, washed with water, then packedinto a heat seal pack and treated at 21° C. and 5000 kg/cm² for 10minutes in a high pressure treatment apparatus. Then, this was heated at121° C. for 20 minutes in a heat sterilizer. This operation enabledcomplete gelation and sterilization simultaneously. The probe couplingmedium thus prepared was used for ultrasonography, whereupon a clearersharper image was obtained compared with the case of no coupling mediumused.

Example 3-1

Three point five parts by weight of curdlan (Takeda Chemical Industries,Ltd.) were dissolved in 96.25 parts by weight of a 25 mM sodiumhydroxide solution, then 0.25 part by weight of ethylene glycoldiglycidyl ether (Denacol EX-810P Medical Grade; Nagase Chemicals Ltd.)was added and the mixture was sufficiently agitated. This wassufficiently deaerated under a vacuum, then was gently poured into amold and was once again deaerated under a vacuum. The result was thenheated at 121° C. for 20 minutes for gelation. The gel was cooled, thenimmersed in an equimolar amount of a hydrochloric acid solution andneutralized with shaking for 24 hours. After the neutralization, theexternal solution was replaced with a physiological saline solution andthe result was washed for 24 hours with shaking once again. The thusobtained gel was sealed in a suitable heat seal pack and was heated at121° C. for 20 minutes for sterilization.

The gel thus prepared was measured for its acoustic property, as aresult of which values of a sound velocity of 1503 m/s and anattenuation rate of 0.13 dB/MHz•cm were obtained. Further, it wasmeasured for its physical properties by a rheometer (made by Fudo KogyoCo.; NRM-2010 J-CW), whereupon the physical properties of the thusprepared cross-linked curdlan gel were found to be a breaking intensityof 3.852×10³ g/cm and a Young's modulus of 5.067×10⁶ dyn/cm². Comparedwith uncrosslinked curdlan gel, the Young's modulus was about the same,but the breaking intensity was improved.

In ultrasonographic image using the above cross-linked curdlan gel, aclearer sharper image was obtained compared with the case of no use ofthe gel.

Further, the above-mentioned cross-linked curdlan gel was immersed in aphysiological saline solution, stored at 5° C., 25° C., and 50° C., andevaluated as to its stability, whereupon no visible changes could beobserved even after three months.

Example 3-2

Five parts by weight of curdlan were dissolved in 94 parts by weight ofa 25 mM sodium hydroxide solution, then 1 part by weight of divinylsulfone was added, the mixture was agitated, then the mixture was heatedat 100° C. for 10 minutes. The semigelatinous substance obtained by theabove procedure was homogenized while adding an equimolar amount of a 1Nhydrochloric acid solution. The homogenized sol was poured on a plate ofa thickness of 10 mm and was frozen at-20° C. for 12 hours, wasfreeze-dried for 48 hours, then was pulverized to obtain thecross-linked curdlan powder.

Ninety-two parts by weight of water were added to 1 part by weight ofthe cross-linked curdlan powder and 7 part by weight of curdlan powderand the mixture was agitated at 13,000 rpm for 10 minutes by a highspeed homogenizer to obtain a homogeneous dispersion. This wassufficiently deaerated under a vacuum, then was gently poured into amold and once again deaerated under a vacuum, then was heated at 100° C.for 10 minutes for gelation. This was cooled and taken out from themold, then was heated at 121° C. for 20 minutes to perform completegelation and sterilization simultaneously.

In ultrasonographic image using the above gel, a clearer sharper imagewas obtained compared with the case of no use.

Example 3--3

Exactly the same procedure was followed as in Example 3-2 to obtain across-linked curdlan powder except that the cross-linking agent waschanged to epichlorohydrin. Ninety-six point five parts by weight ofwater were added to 3.5 parts by weight of the cross-linked curdlanpowder and the mixture was agitated for 10 minutes by a high speedhomogenizer. This was sufficiently deaerated under a vacuum, then waspoured into a mold and heated at 100° C. for 10 minutes for gelation.This was cooled and taken out from the mold, then was taken out andheated at 121° C. for 20 minutes in a heat sterilizer. This procedureenabled complete gelation and sterilization.

In ultrasonography using the above gel, a clearer sharper image wasobtained compared with the case of no use of the gel.

Example 3-4

A 96.998 part by weight amount of 50 mM NaOH solution was added to 2.7parts by weight of curdlan and 0.3 part by weight of alginic acid andthe mixture was agitated at 13,000 rpm for 5 minutes in a high speedhomogenizer. The agitation was then stopped, 0.002 part by weight ofdivinyl sulfone was added, then agitation was performed once again at6,000 rpm for 5 minutes. The result was deaerated under a vacuum, thenwas poured into a mold and heated at 121° C. for 10 minutes forgelation. The gel was cooled and taken out of the mold, then wasimmersed in a 10% calcium chloride solution for gelation of the alginicacid. At this time, 0.1N HCl was added dropwise at suitable times toadjust the pH of the calcium chloride solution to 6 to 7. After 24hours, the gel was taken out and washed with water, then was immersed ina physiological saline solution for 48 hours. Next, a heat sterilizerwas used to heat the gel at 121° C. for 20 minutes to sterilize it.

The thus prepared probe coupling medium was used for ultrasonography,whereupon a clearer sharper image was obtained compared with the case ofno coupling medium used.

Example 4-1--1

Ninety-six point five parts by weight of 170 to 510 mM boric acidsolutions (pH 7.4) were added to 3.5 parts by weight of curdlan powder(made by Takeda Industries Co., Ltd.) and the mixtures were agitated for10 minutes at 13,000 rmp by a high speed homogenizer (made by NipponSeiki Co., Power Homogenizer, PM-1) to obtain homogeneous dispersions.These were sufficiently deaerated under a vacuum, then were gentlypoured into molds, were once again deaerated under a vacuum, and thenwere heated at 80° C. for 20 minutes for gelation. The thus obtainedgels were sealed in suitable heat seal packs and were heated at 121° C.for 20 minutes in a heat sterilizer (made by Tomy Seiko; autoclave,SS-245) for sterilization. The thus prepared gels were measured fortheir breaking strengths and Young's modulus using a rheometer (made byFudo Kogyo Co.; NRM-2010J-CW). The results are shown in FIG. 3 and FIG.4.

A look at the physical properties of the thus prepared boric acid-addedcurdlan gels shows a trend of a rise in the breaking intensity andYoung's modulus along with an increase in the amount of boric acidadded, but the breaking intensity became maximum near 400 mM. With anyfurther addition, the strength conversely fell. Further, to evaluate thetransparency, the curdlan gels prepared above were diced to 20×20×1 mmand the absorbances at 660 nm and transmittance were measured by aspectrophotometer (made by Japan Spectroscopic Co., Ltd.: V-550). Theresults are shown in Table 4-1.

                  TABLE 4-1                                                       ______________________________________                                        Evaluation of Transparency (Effect of                                         Addition of Boric Acid)                                                       Boric acid (mM)    ABS.sub.660                                                                           T %                                                ______________________________________                                        510                0.046   89.9                                               408                0.031   93.0                                               374                0.034   92.6                                               340                0.030   93.3                                               306                0.031   93.0                                               272                0.030   93.3                                               170                0.064   86.4                                                0                 0.288   51.6                                               (Comp. Example)                                                               ______________________________________                                    

From the results of Table 4-1, it is learned that the transparency isimproved by addition of boric acid to curdlan. Further, the absorbancevalue became extremely small in the range of the addition of 272 to 408mM of boric acid. With any further addition, the transparency dropped.

In ultrasonographic image using the above boric acid-added curdlan gel,a clearer sharper image was obtained compared with the case of no use ofthe gel.

That is, a high correlation was observed between the transparency of thegel and the ultrasonographic image and it was confirmed that a sharpimage can be obtained in ultrasonography using the transparent gelaccording to the present invention.

Example 4-1-2

Ninety-six point five parts by weight of water were added to 3.5 partsby weight of curdlan powder and the mixture was agitated in a high speedhomogenizer for 10 minutes. The curdlan-water dispersion obtained wasfully deaerated under a vacuum, then poured into a mold and heated at80° C. for 20 minutes to cause gelation. Next, the gel was cooled andtaken out from the mold, then heated at 121° C. for 20 minutes in a heatsterilizer to cause complete gelation and sterilization.

The thus prepared gel was measured for its physical properties andtransparency in the same way as in Example 4-1--1. The results are shownin FIG. 3, FIG. 4, and Table 4-1. In ultrasonographic image diagnosisusing this, the picture was little hazy and somewhat unclear.

Example 4-2

Two to 10 parts by weight of curdlan were added to 340 mM boric acidsolutions (adjusted to pH of 7.4 by NaOH) and the same procedure wasfollowed as in Example 4-1--1 to agitate the mixtures by a high speedhomogenizer and obtain homogeneous dispersions. These were deaeratedunder a vacuum, then poured into molds and again deaerated under avacuum, then were heated at 80° C. for 10 minutes to cause gelation.After cooling, the results were taken out from the molds and heated at121° C. for 20 minutes to cause complete gelation and sterilizationsimultaneously. The gels were allowed to cool at room temperature, thenwere diced to 20×20×1 mm. The absorbances at 660 nm and thetransmittances were measured using a spectrophotometer (made by JapanSpectroscopic Co., Ltd., V-550).

                  TABLE 4-2                                                       ______________________________________                                        Evaluation of Transparency (Effect of                                         Concentration of Curdlan)                                                     Curdlan                                                                       concentration                                                                 (wt %)           ABS.sub.660                                                                           T %                                                  ______________________________________                                        2                0.092   81.0                                                 2.5              0.061   86.9                                                 3                0.042   90.8                                                 3.5              0.029   93.6                                                 4                0.029   93.6                                                 4.5              0.022   95.1                                                 5                0.014   97.0                                                 6                0.028   93.7                                                 7                0.032   93.0                                                 8                0.034   92.5                                                 9                0.033   92.6                                                 10               0.043   90.5                                                 ______________________________________                                    

It became clear that as the amount of addition of curdlan increased, thegels became stronger and harder. Further, the transparency was improvedthe most with a curdlan concentration of 5% by weight. Inultrasonography using the above gels, clearer, sharper images could beobtained compared with the case of no use.

Example 4-3

Portions of boric acid solutions of varying pH's (6.2, 6.6, 7.0, 7.4,7.6, 7.8, 8.0) were added to 3.5 part by weight amounts of curdlan togive isotonic concentrations and the same procedure was followed as inExample 4-1--1 to obtain boric acid-added curdlan gels at differentpH's. These were heated and sterilized at 121° C. for 20 minutes, thenthe physical properties were measured. The results are shown in FIG. 7.Further, the transparencies of the gels were found by allowing the heatsterilized gels to cool at room temperature, dicing them to 20×20×1 mm,and measuring the absorbances at 660 nm and transmittances by aspectrophotometer (made by Japan Spectroscopic Co., Ltd., V-550). Theresults are shown in Table 4-3. As clear from these results, thebreaking intensity was highest at a pH of 7.6 and the Young's modulus ata pH of 7.8. Further, the transparency was most improved at a pH of 7.4.

                  TABLE 4-3                                                       ______________________________________                                        Evaluation of Transparency (Effect of pH)                                     pH             ABS.sub.660                                                                           T %                                                    ______________________________________                                        6.2            0.142   72.0                                                   6.6            0.070   85.2                                                   7.0            0.042   90.8                                                   7.4            0.022   95.0                                                   7.6            0.026   94.2                                                   7.8            0.096   80.3                                                   8.0            0.174   67.0                                                   ______________________________________                                    

Example 4--4

Ninety-two parts by weight of a 750 mM phenylboric acid solution wasadded to 8 parts by weight of curdlan and the mixture was agitated for10 minutes by a high speed homogenizer. The result amt mixture wasdeaerated under vacuum, then poured into a mold and heated at 70° C. for30 minutes for gelation. The result was cooled and taken out from themold, then was heated at 121° C. for 20 minutes in a heat sterilizer.This operation enabled more complete gelation and sterilization. Inultrasonography using the obtained gel, a clearer sharper image wasobtained compared with the case of no coupling medium used.

Example 4-5

Ninety-seven parts by weight of a 300 mM boric acid solution (adjustedto pH of 7.6 by NaOH) was added to 2.7 parts by weight of curdlan and0.3 part by weight of alginic acid and the mixture was agitated at13,000 rpm for 5 minutes by a high speed homogenizer. The result wasdeaerated under a vacuum, then poured into a mold and heated at 80° C.for 10 minutes for gelation. The result was cooled and taken out fromthe mold, then was immersed in a 10 percent calcium chloride solutionfor 24 hours to cause gelation of the alginic acid. Next, a heatsterilizer was used for heating and sterilization at 121° C. for 20minutes. The resultant probe coupling medium was used forultrasonography, whereupon a clearer sharper image was obtained comparedwith the case of no coupling medium used.

Example 4-6

Ninety-seven point five parts by weight of a 500 mM boric acid solution(adjusted to pH of 7.2 by NaOH) was added to 2 parts by weight ofcurdlan and 0.5 part by weight of lentinan (made by Ajinomoto Co.) andthe mixture was agitated at 13,000 rpm for 5 minutes by a high speedhomogenizer. The result was deaerated under a vacuum, then poured into amold and heated at 100° C. for 10 minutes for gelation. Next, a heatsterilizer was used for sterilization at 121° C. for 20 minutes. Theresultant probe coupling medium was used for ultrasonography, whereupona clearer sharper image was obtained compared with the case of nocoupling medium used.

Example 4-7

Ten grams of scleroglucan (made by San-Ei Gen F.F.I, Inc.) weredissolved in 10 liters of 0.03M NaIO₄ and the result was allowed tostand at 5° C. for five days. Next, 500 ml of ethylene glycol were addedand the mixture agitated, then dialysis was performed at 5° C. for twodays. Ammonia water was added to the dialyzed solution to make it weaklyalkaline, then 5 g of NaBH₄ were added and the mixture was allowed tostand. Next, this was neutralized by 1N acetic acid, then once againdialyzed against flowing water at 5° C. and evaporated to dryness. Thethus prepared powder was digested by β-1,3 glucanase, then thedecomposed product solution was spotted on No. 50 filter paper (made byToyo Roshi Kaisha Ltd.) and developed by n-butanol/iso-propanol/water=3:12:4, whereupon it became clear that the product was curdlan-likeβ-1,3 glucan with about 95% of the β-1,6 bond side chains removed.Ninety-two parts by weight of 340 mM boric acid solution (pH 7.4) wereadded to 8 parts by weight of this product and the mixture was agitatedfor 10 minutes by a high speed homogenizer. The mixture was sufficientlydeaerated under a vacuum, then was poured into a mold and heated at 80°C. for 20 minutes for gelation. The gel was cooled and taken out fromthe mold, then was heated at 121° C. for 20 minutes in a heatsterilizer, whereby complete gelation and sterilization were performed.The probe coupling medium obtained was used for ultrasonography,whereupon a clearer sharper image was obtained compared with the case ofno coupling medium used.

Field of Utilization in Industry

The coupling medium for a probe of an ultrasonograph according to thepresent invention is composed of a gel with a high water content and hasextremely superior ultrasonographic property and mechanical strength.Further, it uses natural polysaccharides as a raw material, so is highin safety and further is available at low cost in large quantities.Further, an ordinary heat sterilization apparatus can be used, sosterilization is also easy. In addition, the probe coupling medium ofthe present invention can be directly affixed to the probe of anultrasonograph using a suitable connection part, so the ease of use isconsidered to be far more improved compared with those in the past.

We claim:
 1. A coupling medium for a probe of an ultrasonographcomprising a gel composing 1-10% by weight of β-1,3 glucan and water. 2.A coupling medium as set forth in claim 1, wherein the concentration ofthe β-1,3 glucan is 1 to 10% by weight, the sound velocity is 1480 m/sto 1550 m/s, and the attenuation rate is not more than 0.3 dB/MHz•cm. 3.A coupling medium as set forth in claim 3, wherein said β-1,3 glucan iscurdlan.
 4. A coupling medium as set forth in claim 1, which contains atleast one compound selected from the group consisting of sodium orpotassium salts of inorganic salts or organic acids, sodium choride,saccharides, and urea.
 5. A coupling medium as set forth in claim 1,which contains at least one polymer substance selected from the groupconsisting of alginic acid, carrageenan, agar--agar, glucomannan,starch, hyaluronic acid, cellulose, methylcellulose, ethylcellulose,nitrocellulose, and polyvinyl alcohols.
 6. A coupling medium as setforth in claim 1, wherein said gel is obtained by a high pressuretreatment.
 7. A coupling medium as set forth in claim 6, wherein theconcentration of the β-1,3 glucan is 1 to 10% by weight, the soundvelocity is 1480 m/s to 1550 m/s, and the attenuation rate is not morethan 0.3 dB/MHz•cm.
 8. A coupling medium for a probe of anultrasonograph as set forth in claim 6, wherein the high pressuretreatment condition is at least 100 kg/cm².
 9. A coupling medium as setforth in claim 6, wherein said β-1,3 glucan is curdlan.
 10. A couplingmedium as set forth in claim 1, wherein at least a portion of the gel ischemically cross-linked.
 11. A coupling medium as set forth in claim 10,wherein the concentration of the β-1,3 glucan is 1 to 10% by weight. 12.A coupling medium as set forth in claim 10, wherein the cross-linkingagent is contained in an amount of 0.001 to 2% by weight based upon thetotal weight thereof.
 13. A coupling medium as set forth in claim 10,wherein said β-1,3 glucan is curdlan.
 14. A coupling medium as set forthin claim 10, wherein said cross-linking agent is at least onecross-linking agent selected from the group consisting of polyhydricglycidylether compounds, polyhydric aziridine compounds, polyhydricamine compounds, polyhydric isocyanate compounds, halomethyl oxiranecompounds and aldehydes, and divinyl sulfone.
 15. A coupling medium asset forth in claim 1, wherein said gel further contains a complexforming compound which can form a complex with β-1,3 glucan.
 16. Acoupling medium as set forth in claim 15, wherein the concentration ofthe β-1,3 glucan is 1 to 10% by weight.
 17. A coupling medium as setforth in claim 15, wherein the concentration of the complex formingcompound is 5 to 900 mM.
 18. A coupling medium as set forth in claim 15,wherein said β-1,3 glucan is curdlan.
 19. A coupling medium as set forthin claim 15, wherein the complex forming compound is boric acid.